Luminescence techniques in radiation dosimetry have traditionally been dominated by thermal methods in which a sample (a thermoluminescence dosimeter, or TLD) is exposed of radiation and is then heated in the dark. At a certain temperature, or within a certain temperature range (either of which is dependent upon the material used and the detailed parameters of the heating procedure), luminescence is emitted from the material. The intensity (for example, the integrated light emission between two specified temperatures) is related, by calibration procedures, to the original absorbed dose of radiation. This method of radiation dosimetry has been described in the literature, and has been in general usage, for approximately five decades.
However, in many circumstances OSL has proven to be a superior method of measuring radiation dose. Generally speaking, OSL methods irradiate a dosimeter with light of a particular frequency and intensity. This exposure excites light production within the dosimeter by transfer of charges from traps to luminescent centers. Then, by measuring intensity and duration of the resulting luminescence decay that is emitted from the dosimeter, an accurate measure may be obtained of the amount of radiation to which the dosimeter was exposed.
As useful as OSL has proven to be, its conventional application has certain shortcomings. More particularly, there is a general departure from linearity in the luminescence/dose curve at higher dose levels and it is susceptible to saturation effects. Further, conventional OSL is not suitable for use in real-time measurement of radiation dose such as would be useful in the treatment of medical disorders by radiation.
Methods and dosimeters employing optically stimulated luminescence in the detection of radiation exposures are described in U.S. Pat. Nos. 5,892,234; 5,962,857; 6,316,782; and 6,414,324, which patents are incorporated herein by reference as if fully set out at this point.
Heretofore, as is well in the radiation dosimetry industry, there has been a need for an invention that provides a method for extending the upper limit of measurable absorbed radiation doses during irradation. Accordingly it should now be recognized, as was recognized by the present inventors, that there exists, and has existed for some time, a very real need for a system and method that would address and solve the above-described problems.
Before proceeding to a description of the present invention, however, it should be noted and remembered that the description of the invention which follows, together with the accompanying drawings, should not be construed as limiting the invention to the examples (or preferred embodiments) shown and described. This is so because those skilled in the art to which the invention pertains will be able to devise other forms of this invention within the ambit of the appended claims.